sigaltstack(2)							System Calls Manual						    sigaltstack(2)

NAME

       sigaltstack - set and/or get signal alternate stack context.

SYNOPSIS

DESCRIPTION

       The  function allows a process to define and examine the state of an alternate stack for signal handlers. Signals that have been explicitly
       declared to execute on the alternate stack will be delivered on the alternate stack.

       If ss is not a null pointer, it points to a structure that specifies the alternate signal stack that will take effect upon return from  The
       ss_flags member specifies the new stack state. If it is set to the stack is disabled and ss_sp and ss_size are ignored. Otherwise the stack
       will be enabled, and the ss_sp and ss_size members specify the new address and size of the stack.

       The range of addresses starting at ss_sp, up to but not including ss_sp+ss_size, is  available to the implementation for use as the  stack.
       This interface makes no assumptions regarding which end is the stack base and in which direction the stack grows as items are pushed.

       If  oss	is not a null pointer, on successful completion it will point to a structure that specifies the alternate signal stack that was in
       effect prior to the call to The ss_sp and ss_size members specify the address and size of that stack. The  ss_flags  member  specifies  the
       stack's state, and may contain one of the following values:

	      SS_ONSTACK	       The  process is currently executing on the alternate signal stack.  Attempts to modify the alternate signal
				       stack while the process is executing on it fails. This flag must not be modified by processes.

	      SS_DISABLE	       The alternate signal stack is currently disabled.

       The value is a system default specifying the number of bytes that would be used to cover the usual case when manually allocating an  alter-
       nate  stack  area. The value is defined to be the minimum stack size for a signal handler.  In computing an alternate stack size, a program
       should add that amount to its stack requirements to allow for the system implementation overhead. The constants and are defined in

       After a successful call to one of the functions, there are no alternate signal stacks in the new process image.

RETURN VALUE

       Upon successful completion, returns 0. Otherwise, it returns -1 and sets to indicate the error.

ERRORS

       The function will fail if:

	      [EINVAL]		       The ss argument is not a null pointer, and the ss_flags member pointed to by ss contains flags other than

	      [ENOMEM]		       The size of the alternate stack area is less than

	      [EPERM]		       An attempt was made to modify an active stack.

WARNINGS

       At HP-UX release 11i Version 1.6 and forward, use of in threads created with process contention scope will result  in  undefined  behavior.
       This function will continue to be reliable in threads created with system contention scope.

APPLICATION USAGE

       The following code fragment illustrates a method for allocating memory for an alternate stack:

       In  some  implementations, a signal (whether or not indicated to execute on the alternate stack) will always execute on the alternate stack
       if it is delivered while another signal is being caught using the alternate stack.

       On some implementations, stack space is automatically extended as needed. On those implementations, automatic extension	is  typically  not
       available for an alternate stack. If the stack overflows, the behavior is undefined.

   Threads Considerations
       Each thread may define an alternate signal handling stack.

   LWP (Light Weight Processes) Considerations
       Each LWP may define an alternate signal handling stack.

SEE ALSO

       sigaction(2), setjmp(3C), <signal.h>.

CHANGE HISTORY

       First released in Issue 4, Version 2.

																    sigaltstack(2)